Angle measuring devices measuring the tightening angle are known in the prior art for a rotary-angle-controlled tightening of bolts or nuts. In doing so a screwed connection is tightened, for example by a torque wrench, until a predefined snug point torque is achieved. With achievement of the snug point torque the screwed connection is snugly fitted, i.e. all involved elements such like a bolt head, a nut and parts to be connected smoothly abut to each other after flattening all roughness. Subsequently another tightening operation is carried out by a further rotation according to a certain predefined rotary angle. Thus an optimal pretension of the screwed connection is achieved.
It is known in the art to connect mechanical angle measuring devices easy releasable to an operating tool. For example the German document DE 296 22 318 U1 discloses a mechanical rotary angle measurement disk comprising an angle measuring disk and an angle pointer element. The angle measuring disk is coupled to an operating tool at the rotary axis und hence follows a rotary motion of the operating tool. The angle pointer element is fixed to a work part via a support arm and reference arm respectively, thus remaining in a starting position during a rotary motion of the operating tool. A performed rotary angle is indicated to a user by the angle pointer element on the angle measuring disk.
A disadvantage of the known mechanical angle measuring devices is that they are applied directly at the position of a screwed connection requiring an adequate amount of working space. The reference arm must also be applicable and fixed respectively in the close of the screwed connection. Thus the field of application of the known mechanical angle measurement devices is restricted. Furthermore the application of the reference arm increases the amount of work on a screwed connection for a user. Moreover there is no automatic documentation of measured rotary angles possible with the known mechanical angle measuring devices.
Electronic torque wrenches with an integrated electronic measurement of a rotary angle are also known, for example from the German document DE 296 15 123. These electronic torque wrenches enable a torque measurement as well as a measurement of a rotary angle and hence are particularly suitable for a rotary-angle-controlled tightening of bolts or nuts. However, the angle measuring device of these torque wrenches is integrated non-releasable within the torque wrench with the detrimental effect that they can not be used with other operating tools.